Short answer
Mahr should be agreed responsibly and should not become a meaningless figure that neither side realistically intends to honor.
Islamic Guidance
What Islam teaches
Mahr is a genuine right of the wife. It should be discussed honestly and documented clearly, with both parties understanding the obligation.
Practical Guidance
What you can consider
Agree on an amount that reflects the circumstances and is clearly understood. The husband should treat it as a real obligation rather than merely a ceremonial number.
Sources
Qur'an 4:4.